Titanium dioxide can be widely controlled in its particle diameter from micron-size to nano-size, and its particle shape includes various shapes such as particulate shape, nearly spherical shape and spherical shape, and, in addition, acicular shape, spindle shape and platy shape. For example, titanium dioxide having a particle diameter of about 0.15-0.25 μm is excellent in hiding power and coloring power and chemically stable, and hence is used in a wide variety of the fields as white pigments. Fine particle titanium dioxide of less than about 0.1 μm shows transparency and screens ultraviolet rays when incorporated in a resin, and hence used as a transparent pigments, and acicular titanium dioxide having a length of 1-10 μm and a ratio of length to diameter (axial ratio) of 3 or higher is used as special pigments lowered in coloring power or a loading material.
When an electroconductive layer is formed on the surface of such titanium dioxide, electroconductivity can be given to titanium dioxide which is originally an insulator, and the titanium dioxide is used as electroconductivity imparting agents or antistatic agents for glass, ceramic articles such as toners for electrophotography, plastic articles such as polymer molded products and polymer films, and paper articles such as electrophotographic copying papers and electrostatic recording papers. The reasons for using titanium dioxide as base particles on which an electroconductive layer is formed are that the amount of the electroconductive materials necessary for obtaining the desired electroconductivity can be reduced and, furthermore, titanium dioxide has various particle diameters or particle shapes as mentioned above, and functionality of titanium dioxide can be optionally selected depending on sites of use of the electroconductivity imparting agents. For example, when white pigment titanium dioxide is used as base particles, a white electroconductive powder is obtained, and when fine particle titanium dioxide is used as base particles, a transparent electroconductive powder is obtained, and when acicular titanium dioxide is used as base particles, the electroconductivity can be made efficient by utilizing the anisotropy in shape.
For the electroconductive layer formed on the surface of titanium dioxide, there has been widely used tin oxide doped with antimony because it has excellent electroconductivity and, besides, is less in change of electroconductivity with time (see, for example, Patent Document 1). However, recently the toxicity of antimony is feared, and researches on electroconductive powders containing no antimony have been conducted, resulting in development of tin oxide doped with phosphorus in place of antimony (see, for example, Patent Documents 2 and 3).
Patent Document 1: JP-B-6-17231
Patent Document 2: Patent No.3357107
Patent Document 3: Patent No.3365821